فَتَنَحَّى الرَّجُلُ، وَجَعَلَ يَهْتِفُ وَيَبْكِي، فَقَالَ لَهُ رَسُولُ اللَّهِ ﷺ: «أَمَا تَقْرَأُ قَوْلَ اللَّهِ عَزَّ وَجَلَّ: ﴿وَنَضَعُ الْمَوَازِينَ الْقِسْطَ لِيَوْمِ الْقِيَامَةِ فَلَا تُظْلَمُ نَفْسٌ شَيْئًا وَإِنْ كَانَ مِثْقَالَ حَبَّةٍ مِنْ خَرْدَلٍ أَتَيْنَا بِهَا وَكَفَى بِنَا حَاسِبِينَ﴾».
Translation: The man stepped aside and wept. The Prophet ﷺ reminded him of Allah's words: On the Day of Resurrection the scales of justice will be set up; no soul will be wronged at all, and even a deed as small as a mustard seed will be brought forth. Allah is sufficient as Reckoner. (Al-Anbiyāʾ 21:47)
Al-qisṭ means justice. “The weight of a mustard seed” illustrates how even very small matters are not lost in the final reckoning.